<!doctype html>
<html>
	<head>
		<meta charset="uft-8">
		<title></title>
		<style>
			#d1{
				width:300px;height:200px;
				background:#f00;
				float:left;
			}
			#d2{
				width:200px;height:300px;
				background:#0f0;
				float:left;
			}
			#d3{
				width:250px;height:250px;
				background:#00f;
				float:left;
			}
			#d4{
				height:50px;
				background:#000;
				clear:both;
				/*当前元素不会被任何浮动元素遮挡*/
			}
		</style>
	</head>
	<body>
		<div id="d1"></div>
		<div id="d2"></div>
		<div id="d3"></div>
		<div id="d4"></div>
	</body>
</html>